U.S. Pat. No. 6,783,527 (Aug. 31, 2004), which the instant application incorporates by reference, broadly discusses two significant uses of a panel of granular material: (1) for filtering a dusty gas, the filtration being assisted by an accumulation of dust deposits (filter cakes) upon gas-entry faces of the granular material; (2) for countercurrent contacting of the granular material with a gas. For gas filtration, U.S. Pat. No. 7,033,556 (Apr. 25, 2006), also incorporated herein by reference, discloses an improved arrangement (broadly speaking, a new kind of “panel bed”) that employs vertically mounted filter trays for cleaning a dusty gas. See also “Granular-bed filtration assisted by filter-cake formation: 4. Advanced designs for panel-bed filtration and gas treating,” by A. M. Squires, Powder Technology, vol. 155, pp. 74-84, 2005.
The referenced patents disclose means for renewing gas-entry faces of a panel bed of a granular material in which either filter trays or vertically disposed louvers (resembling slats of a Venetian blind) support the material. One means is to provide a “reverse” surge flow of gas toward the gas-entry faces (a “puffback”). This surge flow produces a body movement of the granular material toward the faces, spilling moieties of the material from the faces and concomitantly exposing previously underlying material, thereby renewing the faces. In experiments, at both the small and large scales, effecting the requisite reverse surge flow of gas has been accomplished by releasing gas from a tank holding gas at a pressure substantially higher than the panel bed's ambient pressure. Provided are a tank, a quick-opening valve for releasing the elevated-pressure gas therein, and duct work to carry the resultant surge flow of gas to the space that, in normal operation of the panel bed, receives treated gas; tank, valve, and duct work are external to this space.